Ofdma-tdma-based seismic data transmission over tv white space

ABSTRACT

A system, computer-readable storage medium and method of reflection seismic survey in a wireless seismic network within a survey area is described. The method includes detecting, in each of a plurality of wireless seismic sensor nodes, seismic reflection signals from a seismic energy source; recording, in each of a plurality of wireless geophones, detected seismic signals; transmitting, by the geophones, the recorded seismic signals as digital data, using a combination of Orthogonal Frequency-Division Multiple Access (OFDMA) and Time Division Multiple Access (TDMA), to a central data receiving device; changing the seismic energy source location for seismic reflection; and repeating the detecting, recording and transmitting a number of times for each change in seismic energy source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to provisionalapplication No. 63/293,905 filed Dec. 27, 2021, the entire contents ofwhich are incorporated herein by reference.

STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in an article “OFDMA-TDMA-BasedSeismic Data Transmission Over TV White Space,” IEEE CommunicationsLetters (May 2021). The article was published Jan. 18, 2021, and isherein incorporated by reference in its entirety.

STATEMENT OF ACKNOWLEDGEMENT

The author would like to acknowledge the support provided by theDeanship of Scientific Research (DSR) at King Fahd University ofPetroleum & Minerals (KFUPM), Dhahran, Saudi Arabia, for funding thiswork.

BACKGROUND Technical Field

The present disclosure is directed to a system, computer-readablestorage medium and method of transmission of the seismic data based on acombination of OFDMA and TDMA schemes for seismic data acquisitionsystems. Channel parameters related to the OFDMA-TDMA scheme such astime slot and OFDMA sub-carriers assigned to a geophone can behardwired. The OFDMA subcarriers and time shot assigned to a geophonematch with data acquisition parameters, like bandwidth, samplingfrequency, bits per sample, and trace (seismic data recorded by ageophone) duration of the seismic data.

Description of Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentdisclosure.

A seismic survey is an important tool for exploring for subsurfacemineral deposits, volcanic monitoring, landslide monitoring, monitoringof glaciers, underground tomography, and earthquake prediction. Theseismic survey is performed by sending seismic waves into the deepsubsurface of the Earth, and recording the reflected and refracted wavesas seismic data. The acquisition of seismic data requires specialdevices such as vibration trucks and geophones. After processing andanalyzing the acquired data, the seismic survey is configured to providean insight into the geological structure of the Earth, without using anycostly drilling method.

In a traditional approach, a network of sensors called “geophones” aredeployed in a survey area that is connected to a center communicationpoint via a cable for communicating data. However, this approachincludes various disadvantages such as excess weight, reliabilityissues, complexities in deployment and maintenance, human resourcecosts, and other operational costs. Moreover, cables are prone to damageby stress, resulting in more frequent downtime of the seismic survey.

Oil and gas operators are focusing on increasingly complex hydrocarbonreservoirs that are often difficult to image. Such targets requireincreasing amounts of data in order to acquire the most accuratepossible image of the subsurface. To meet the growing need and demandfor massive volumes of data, geo-physical service companies areimproving systems to provide more recording channels per survey.

Geo-physical service companies perform surveys utilizing a large numberof wired geophones, for example on the order of 200,000 to over amillion wired geophones.

In recent years, wireless seismic data acquisition systems have startedto address an increased demand for better subsurface image quality datahaving low transmission time. The wireless system utilizes seismicsensor nodes equipped with wireless transceivers to form a network ofwireless geophone sensors. However, the transmissions are made eitherdirectly between each wireless geophone and a control station ordirectly between each wireless geophone and a concentrator, which leadsto congestion in the network and low transmission rate. For example, aland seismic exploration of 10,000 to 30,000 geophones, covering an areaon the order of several square kilometers, has an average density of upto 2000 devices per km². That amount of traffic or connections in asurvey is similar to what a telecommunication operator would handle ifeveryone in a low-populated city placed a call at substantially the sametime.

Recently, wireless seismic network architectures have been proposedbased on random access techniques, like Carrier Sense Multiple Access(CSMA)-based protocols. CSMA works well for a small network (local area)having few nodes. However, when it comes to a large regional area havinga large number of nodes, transmission needs to be scheduledappropriately, requiring enhanced transmission time which results inreduced throughput. The rate at which data are generated by a geophonedepends on the signal sampling interval/frequency and the resolution ofthe A/D converter used. For a survey with a minimum sample intervalT_(s) of 0.5 ms and a 24 bit A/D converter resolution, each geophone inthe network will generate data at rate of 48 kbit/s. Data generated bygeophones required to be transmitted to the center unit for each recordor shot could be quite large. This can be quantified by an examplesurvey that entails 30,000 geophones, with seismic signals sampled at0.5 ms interval, 5 s geophone recording period, and a time lapse betweenrecords of 60 s. To keep up with this data throughput, multiple radiolinks are required to share the bandwidth load. This example survey with30,000 geophones transmitting data in real-time will require a sumthroughput of 1.44 Gbit/s per shot. Support for such throughput would because numereous problems for existing wireless sensor networks.

Accordingly, it is one object of the present disclosure to providemethods and wireless geophones for maximizing the throughput of theseismic survey for timely delivery of the seismic data from geophones toa data center.

SUMMARY

In an aspect, a method of reflection seismic survey is in a wirelessseismic network within a survey area. The method includes detecting, ineach of a plurality of wireless seismic sensor nodes, seismic reflectionsignals from a seismic energy source; recording, in each of theplurality of wireless seismic sensor nodes, the detected seismicreflection signals; transmitting, by the wireless seismic sensor nodes,the recorded seismic signals as seismic digital data, using acombination of Orthogonal Frequency-Division Multiple Access (OFDMA) andTime Division Multiple Access (TDMA), to a central data receivingdevice; changing the seismic energy source location for seismicreflection; and repeating the detecting, recording and transmitting anumber of times for each change in seismic energy source.

In another aspect, a system having wireless seismic sensor nodes forreflection seismic survey use a wireless seismic network within a surveyarea of at least 20 km². Each of a plurality of the wireless seismicsensor nodes includes communications circuitry configured to detectseismic reflection signals from a seismic energy source; a memory forrecording the detected reflection seismic signals; and thecommunications circuitry configured to transmit the recorded seismicsignals as seismic digital data, using a combination of OrthogonalFrequency-Division Multiple Access (OFDMA) and Time Division MultipleAccess (TDMA), to a central data receiving device, wherein thedetecting, recording and transmitting is repeated a number of times uponchanging the source location for the seismic reflection signals.

In another aspect, a non-transitory computer-readable storage mediumstores instructions for reflection seismic survey in a wireless seismicnetwork within a survey area. Processing circuitry, in each of aplurality of wireless seismic sensor nodes, executes the instructionsaccording to a method including detecting, in each of a plurality ofwireless seismic sensor nodes, seismic reflection signals from a seismicenergy source; recording, in each of the plurality of wireless seismicsensor nodes, the detected seismic reflection signals; transmitting therecorded seismic signals as seismic digital data, using a combination ofOrthogonal Frequency-Division Multiple Access (OFDMA) and Time DivisionMultiple Access (TDMA), to a central data receiving device; monitoring achange in the seismic energy source location for seismic reflection; andrepeating the detecting, recording and transmitting a number of timesfor each change in seismic energy source.

The foregoing general description of the illustrative embodiments andthe following detailed description thereof are merely exemplary aspectsof the teachings of this disclosure, and are not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of this disclosure and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a perspective view of a wireless seismic network, according toaspects of the present disclosure;

FIG. 2 is a block diagram of a wireless seismic sensor node, accordingto aspects of the present disclosure;

FIG. 3 is a block diagram of a wireless gateway, according to aspects ofthe present disclosure;

FIG. 4 is a flowchart for reflection seismic survey in a wirelessseismic network, according to aspects of the present disclosure;

FIG. 5A illustrates channel assignment to various wireless seismicsensor node using the OFDMA-TDMA scheme, according to aspects of thepresent disclosure;

FIG. 5B illustrates a block diagram of seismic data recording andtransmission at a wireless seismic sensor node, according to aspects ofthe present disclosure;

FIG. 5C illustrates a block diagram of a receiver at a central datareceiving device for a specific time slot, according to aspects of thepresent disclosure;

FIG. 6 is a diagram of a state transition model of seismic datatransmission, according to aspects of the present disclosure;

FIG. 7 is a diagram of a graph of throughput per wireless seismic sensornode versus signal-to-noise ratio, according to aspects of the presentdisclosure;

FIG. 8 is a diagram of a graph of time to transmit data of one shot tothe central data receiving device versus signal-to-noise ratio,according to aspects of the present disclosure;

FIG. 9 is a diagram of a graph of re-transmission by wireless seismicsensor node per M frames (shot) versus signal-to-noise ratio, accordingto aspects of the present disclosure;

FIG. 10 is a diagram of a graph of time to transmit data of one shot tothe central data receiving device versus sampling frequency, accordingto aspects of the present disclosure.

DETAILED DESCRIPTION

In the drawings, like reference numerals designate identical orcorresponding parts throughout the several views. Further, as usedherein, the words “a,” “an” and the like generally carry a meaning of“one or more,” unless stated otherwise.

Furthermore, the terms “approximately,” “approximate,” “about,” andsimilar terms generally refer to ranges that include the identifiedvalue within a margin of 20%, 10%, or preferably 5%, and any valuestherebetween.

Aspects of this disclosure are directed to a method and wirelessgeophones for reflection seismic survey in a wireless seismic networkwithin a survey area of substantially 20 km². In the present disclosure,an Orthogonal Frequency-Division Multiple Access (OFDMA) Time DivisionMultiple Access (TDMA) based seismic data acquisition system is used toachieve a desirable throughput, which ensures timely delivery of theseismic data from a large number of wireless geophones to a data centerdirectly. In an OFDM-TDMA system, a whole OFDM symbol is assigned to onegeophone. In the OFDMA-TDMA system, a sub-carrier in a OFDM symbol isassigned to a geophone and other sub-carriers to other geophones. Inthis way the system can accommodate a much larger number of geophones.In an embodiment, the OFDMA-TDMA system can support up to 136,800geophones, by assigning 1440 data subcarriers and 95 time slots togeophones.

Further, the present disclosure utilizes Television (TV) white space(also known by acronym TVWS) for transmission to have long-distancelinks between the wireless geophones and the data center. Using the TVwhitespace enables substantially removes or eliminates a requirement ofhaving intermediate relays and thereby reducing the delivery time of theseismic data. It is evident from the present disclosure that atransmission time of seismic data per seismic shot is less than thetransmission time achieved by the Carrier Sense Multiple Access (CSMA)technique. Furthermore, the use of TV white space and reducedtransmission saves hardware cost and improves the seismic data deliverytime. The throughput and the transmission time expressions for theOFDMA-TDMA based seismic data acquisition system are derived consideringa Markov chain model. The present disclosure helps design a wirelessseismic network, in particular, to find the seismic shot interval timeand the re-transmissions attempt for a successful data transmission of aseismic shot.

In various aspects of the disclosure, non-limiting definitions of one ormore terms that will be used in the document are provided below.

“TV white space” is an unutilized portion (or vacant channels) of alicensed radio spectrum in the ultra-high frequency (UHF) band between470 and 690 MHZ assigned for television broadcast that may be used bysecondary users in a geographical location. The TV white space may beunlicensed. However, for effective and efficient use of the TVwhitespace radio spectrum the white space needs to be used in acontrolled manner.

The term “seismic shot” may be defined as an event of initiation ofseismic waves in the rocks or subsurface of the Earth by seismic energysource at a known point.

FIG. 1 describes a perspective view of a wireless seismic network(hereinafter interchangeably referred to as “the network 100”),according to aspects of the present disclosure.

Referring to FIG. 1 , the wireless seismic network 100 includes a largenumber of wireless seismic sensor nodes 102, at least one wirelessgateway 104, a seismic energy source 106, and a central data receivingdevice 108.

The seismic energy source 106 is configured to generate and broadcastradio signals (seismic signals) of predetermined frequencies towards thesurface of the Earth. Due to different strata of the Earth, thebroadcasted seismic signals are refracted and reflected. The seismicsurveys are performed by using the refracted and reflected seismicsignals. In some examples, the seismic energy source 106 may be atruck-mounted or buggy-mounted device that introduces seismic signalshaving vibrations/frequencies into the Earth. For example, the seismicenergy source 106 may be a vibrator truck, an air gun, a thumper truck,a plasma sound source, and/or a seismic vibrator boomer source. In anaspect, the seismic energy source 106 may provide seismic signals havingsingle pulses of frequencies or continuous sweeps of the frequencies.

The number of wireless seismic sensor nodes 102 (hereinafterinterchangeably referred to as “wireless geophone 102”) is configured todetect the reflected and/or refracted seismic signals and record thedetected seismic signals. Each of the wireless geophones 102 mainlyincludes two main modules; namely, a data acquisition module and acommunication module (not shown). The data acquisition module isconfigured to record the reflected and/or refracted seismic signals andprocess the recorded seismic signals to generate a seismic digital data.The communication module is used to communicate the seismic digital datato the at least one wireless gateway 104. In an aspect, thecommunication module may employ a smart reconfigurable antenna forcommunicating over the network 100. In an exemplary implementation, thenetwork 100 may include fifty thousand (50,000) or greater wirelessgeophone nodes. Each of the wireless geophones 102 is configured torecord the seismic signals detected in the proximity of each of thewireless geophone 102. In an aspect, the wireless geophone 102 isconfigured to transmit the seismic digital data using a combination ofOFDMA and TDMA, to the central data receiving device 108.

In an embodiment, the at least one wireless gateway 104 may beconfigured to be communicatively coupled to the plurality of wirelessgeophones 102. The wireless gateway 104 may be configured to receive theseismic digital data from each wireless geophone 102 and transmit thereceived seismic digital data to the central data receiving device 108.To save power, the wireless gateway 104 may be configured to form acluster of a number of wireless geophones and receive data from thegeophones of the cluster. The wireless gateway 104 aggregates thereceived seismic digital data from the geophones of the cluster andtransmits the aggregated data to the central data receiving device 108.In an embodiment, the wireless gateway 104 may be configured to transmitthe received seismic digital data after a predetermined time interval ortransmit the received seismic digital data continuously for the realtime processing. In an embodiment, the wireless gateway 104 isconfigured to transmit the seismic digital data, received from thewireless geophones 102, using a combination of OFDMA and TDMA, to thecentral data receiving device 108. In an embodiment, the wirelessgateway 104 is selected from a group consisting of a WAP gateway, an XMLgateway, a HTML gateway, a CHTML gateway, a WML gateway, a Lora gateway,and a ZigBee gateway.

The central data receiving device 108 is configured to receive thetransmitted seismic digital data from the wireless gateway 104 andprocess the received data by translating the received data into usableinformation. In some embodiments, the central data receiving device 108may be placed within a defined range for receptivity, for example, 6miles from the wireless gateway. In some embodiments, the central datareceiving device 108 may be placed more or less than the defined rangedepending on aggregates such as noise, line of site and other aspects.In some embodiments, the central data receiving device 108 may beimplemented in a mobile arrangement such as on a vehicle such as atruck. In some embodiments, the central data receiving device 108 isconfigured to perform various steps such as data preparation, datatransformation, and data validation. In an embodiment, the central datareceiving device 108 is configured to remove the errors introducedduring data transmission. The central data receiving device 108 isfurther configured to store the processed data. The central datareceiving device 108 is configured to store the location of eachwireless geophones 102, the received corresponding seismic digital dataand various other parameters such as depth at which wireless geophone102 is placed, the time at which the wireless geophone was installed,time of arrival of seismic signals at the wireless geophone, etc. In anembodiment, the central data receiving device 108 may include a centralprocessor, a memory, one or more storage devices, and input/outputinterfaces/devices. In some embodiments, the central data receivingdevice 108 may only perform storage function and interface with othersystems for processing. In an embodiment, the central data receivingdevice 108 comprises an electronic computing device operable to receive,transmit, process, store, or manage data and information associated withthe network 100.

The central data receiving device 108 includes an electronic circuit forfiltering and amplification of the received seismic digital data. In anembodiment, the central data receiving device 108 is configured toperform signal denoising, detailed analysis, and based on the results ofthe analysis, a warning is provided to a corresponding authority.

FIG. 2 is block diagram of a wireless seismic sensor node (102, 200),according to aspects of the present disclosure. The wireless seismicsensor node (102, 200) for reflection seismic survey, in the wirelessseismic network 100 is configured to receive/detect seismic signalsreflected and/or refracted from different strata of the Earth. In anembodiment, to perform the seismic survey, a number of wireless seismicsensor nodes (102, 200) are deployed under the surface of the Earth at apredefined depth in a particular area. In an embodiment, the survey areais at least 20 km². As shown in FIG. 2 , the wireless seismic sensornode 200 includes a data acquisition module 202, a communicationscircuitry 212, an antenna 214, and a battery 216.

Further, the wireless seismic sensor node (102, 200) includes a memory(not shown) for recording the detected seismic signals. The memory isconfigured to store time stamped recording of the detected seismicsignals. In an embodiment, the memory is configured to store a set ofrules for processing the received signals. In one embodiment, the memorymay include any computer-readable storage medium known in the artincluding, for example, volatile memory, such as Static Random AccessMemory (SRAM) and Dynamic Random Access Memory (DRAM), and/or anon-volatile memory, such as Read Only Memory (ROM), erasableprogrammable ROM, flash memories, hard disks, optical disks, andmagnetic tapes.

The data acquisition module 202 includes a geophone 204, an analogcircuitry 206, an analog-to-digital (A/D) converter 208, and amicrocontroller 210. In seismic surveys, a relevant data is collected bythe wireless seismic sensor nodes 200. To find the relevancy of thedata, mapping of the reflected signals is performed in space and timedomain. Such reflected signals may have the same frequency as thesignals sent by the seismic energy source 106. Vibrations detected bythe wireless seismic sensor node (102, 200) at other frequencies may bedue to other environmental sources that are of non-interest for theseismic surveys, and hence may be filtered out before any amplification.

The geophone 204 is configured to detect seismic vibrations in anydirection. In an example, the geophone 204 is a ground motion sensorthat converts ground vibrations into an output voltage. The outputvoltage represents the deviation in the ground's motion, which forms araw data that is subsequently processed in order to study the Earth'ssubsurface. The geophone 204 is configured to receive/detect seismicsignals reflected from different layers of the Earth.

In some embodiments, the geophone 204 may be an external device that isseparate from the data acquisition module 202. In such case, thegeophone 204 may be placed directly on the ground. In other embodiments,the geophone 204 is mounted within a weatherproof housing containing thedata acquisition module 202. The weatherproof housing may be made ofplastic or metal, such as galvanized steel. The geophone 204 may beconfigured in a cylindrical container or in the form of a disk.

The analog circuitry 206 is configured to filter the seismic signalsdetected by the geophone 204. After filtering the signal, the analogcircuitry 206 is configured to provide a high voltage gain for preparingthe data to be sampled at high resolution by the analog-to-digitalconverter 208.

The analog-to-digital converter 208 is configured to sample and digitizethe received seismic signals to generate the seismic digital data.

The microcontroller 210 cooperates with the memory to receive andexecute the set of program instructions for processing the receivedsignals. The microcontroller 210 may be implemented as one or moremicroprocessors, microcomputers, digital signal processors, centralprocessing units, state machines, logic circuitries, and/or any devicesthat manipulate signals based on program instructions.

The communications circuitry 212 is commutatively coupled to the dataacquisition module 202 and receives the seismic digital data from thedata acquisition module 202. In an aspect, the communications circuitry212 includes input/output facilities. The communications circuitry 212may be configured to communicate with other wireless geophones, thewireless gateway 104 via the input/output facilities coupled as acircuit arrangement and/or components for enabling input/outputoperations with the communications circuitry 212. In an embodiment, thecommunications circuitry 212 may include at least one antenna fortransmitting and receiving signals. The communications circuitry 212 mayinclude a wireless-frequency transceiver having a variable gainamplifier that generates radio-frequency signals for transmission. Awireless amplifier circuit may be used to amplify the radio-frequencysignals at the output of the variable gain amplifier for transmission.The communications circuitry 212 is configured to transmit the recordedseismic signals as the digital data, using a combination of OFDMA andTDMA, to the central data receiving device 108. In an embodiment, thecommunications circuitry 212 is further configured to transmit theseismic signals such that the OFDMA subcarriers and a time shot assignedto each geophone match data acquisition parameters of the geophone ofbandwidth (frequency range), sampling frequency and sampling rate, bitsper sample, and recorded trace duration of the seismic digital data.

Further, the communications circuitry 212 is configured to preferablytransmit the seismic digital data at a rate of 48 kbit/sec using TDMA.Each subcarrier in OFDMA preferably may have a bandwidth of 3937 Hz, andtwo subcarriers per time slot are assigned to one wireless seismicsensor node (102, 200).

In some embodiments, the communications circuitry 212 is furtherconfigured to wirelessly transmit the seismic digital data using the TVbroadcast bands directly to the central data receiving device 108. In apreferred embodiment, the seismic digital data are transmitted in TVwhite bands (VHF/UHF Bands), where UHF stands for “Ultra High Frequency”while VHF stands for “Very High Frequency.” UHF can range from low band(378-512 MHz) to high band (764-870 MHz) while VHF ranges from low band(49-108 MHz) to high band (169-216 MHz).

The communications circuitry 212 is further configured to transmit theseismic digital data recorded per shot substantially within 10 seconds.In some embodiments, the time slot and subcarriers assigned to eachwireless geophone may be fixed. In some other embodiments, the time slotand subcarriers assigned to each wireless geophone may vary. In anembodiment, the frame size of seismic digital data of a data stream maybe divided into frames, and the frame size is adjusted by thecommunications circuitry 212 based on a signal-to-noise ratio.

In an embodiment, the antenna 214 is configured to transmit the seismicdigital data in a form of signals towards the wireless gateway 104. Inanother embodiment the antenna 214 is configured to receive reflected orrefracted seismic signals from the various layers of the Earth withinthe proximity of the wireless seismic sensor node (102, 200). In oneembodiment, each wireless seismic sensor node (102, 200) may include ashort-range radio transmission antenna. In another embodiment, theantenna is integrated into a casing of the wireless seismic sensor node(102, 200). In a further embodiment, the wireless seismic sensor node(102, 200) may utilize directional radio antenna or antenna array toenhance communication efficiency either when the antenna acts as areceiver or a transmitter. If directionality is desired, a beam antennawith gain such as a three element Yagi or an antenna with a reflectormay be used by the wireless seismic sensor node (102, 200).

In an embodiment, the wireless seismic sensor node (102, 200) has abattery (power source) 216 which is configured to provide power to eachunit and module of the wireless seismic sensor node (102, 200) such thateach unit properly functions. In an embodiment, the power can be used ina controlled manner to achieve extended battery life, without affectingthe working of the wireless seismic sensor node (102, 200). For example,each unit of the wireless seismic sensor node (102, 200) may beconfigured to function at a predetermined time. In an embodiment, thewireless seismic sensor node (102, 200) may have a primary battery and asecond battery. In another embodiment, the battery 216 is selected froma group including a lead acid battery, a lithium-ion battery, and anickel-metal-hydride battery. In some embodiments, the battery 216 maybe a rechargeable battery.

In an embodiment, there may be more than 50,000 wireless seismic sensornodes (102, 200) in the survey area. When the seismic energy source 106moves from one location to another location and broadcasts seismicsignals towards surface of the Earth, the broadcasted seismic signalsare reflected and/or refracted from different strata of the Earth. Eachof the wireless seismic sensor nodes (102, 200) is configured to detectreflected and/or refracted seismic signals and record the detectedseismic signals. Further, each of the wireless seismic sensor nodes(102, 200) is configured to transmit the recorded seismic signals asseismic digital data to the central data receiving device 108.Therefore, more than 50,000 reflected signals are recorded andtransmitted. In an aspect, after one shot, the central data receivingdevice 108 is configured to receive about 50,000 recorded seismicsignals as seismic digital data transmitted by more than 50,000 wirelessseismic sensor nodes (102, 200).

In one embodiment, a wireless seismic sensor node (102, 200) isconfigured with a spike to be inserted into the ground. In a preferableembodiment of the invention, the seismic sensor node has a conicalportion tapering steeply to a flat top and a flat circular bottom. Inthis configuration, much like a spinning top, a determination can bemade remotely whether the seismic sensor node is positioned with itsflat bottom surface in direct contact with the earth, or if the exteriorconical surface is in contact with the earth. A flat bottom surface ispreferably in contact with the earth as a means of better detection andrecordation of seismic signals. In a still further embodiment of theinvention the bottom surface is convex permitting only a bottom rim ofthe cone to be in contact with the earth.

FIG. 3 illustrates a block diagram of a wireless gateway, according toaspects of the present disclosure. In some embodiments, the functionsand processes of the wireless gateway 104 may be implemented by acomputer 326. Next, a hardware description of the computer 326 accordingto exemplary embodiments is described with reference to FIG. 3 . In FIG.3 , the computer 326 includes a CPU 300 which performs the processesdescribed herein. The process data and instructions may be stored in amemory 302. These processes and instructions may also be stored on astorage medium disk 304 such as a hard drive (HDD) or portable storagemedium or may be stored remotely. Further, the embodiments are notlimited by the form of the computer-readable media on which theinstructions of the inventive process are stored. For example, theinstructions may be stored on CDs, DVDs, in FLASH memory, RAM, ROM,PROM, EPROM, EEPROM, hard disk or any other information processingdevice with which the computer 326 communicates, such as a server orcomputer.

Further, the embodiments may be provided as a utility application,background daemon, or component of an operating system, or combinationthereof, executing in conjunction with CPU 300 and an operating systemsuch as Microsoft® Windows®, UNIX®, Oracle® Solaris, LINUX®, ApplemacOS® and other systems known to those skilled in the art.

In order to achieve the computer 326, the hardware elements may berealized by various circuitry elements, known to those skilled in theart. For example, CPU 300 may be a Xenon® or Core® processor from IntelCorporation of America or an Opteron® processor from AMD of America, ormay be other processor types that would be recognized by one of ordinaryskill in the art. Alternatively, the CPU 300 may be implemented on anFPGA, ASIC, PLD or using discrete logic circuits, as one of ordinaryskill in the art would recognize. Further, CPU 300 may be implemented asmultiple processors cooperatively working in parallel to perform theinstructions of the inventive processes described above.

The computer 326 in FIG. 3 also includes a network controller 306, suchas an Intel Ethernet PRO network interface card from Intel Corporationof America, for interfacing with network 324. As can be appreciated, thenetwork 324 can be a public network, such as the Internet, or a privatenetwork such as LAN or WAN network, or any combination thereof and canalso include PSTN or ISDN sub-networks. The network 324 can also bewired, such as an Ethernet network, or can be wireless such as acellular network including EDGE, 3G, 4G, 5G wireless cellular systems.The wireless network can also be WiFi®, Bluetooth®, or any otherwireless form of communication that is known.

In one embodiment, the computer 326 includes a broadcast TV receiver anda tuner 330 to wirelessly communicate with multiple wireless Geophonesover a TV broadcast signal.

The computer 326 further includes a display controller 308, such as aNVIDIA® GeForce® GTX or Quadro® graphics adaptor from NVIDIA Corporationof America for interfacing with display 310, such as a Hewlett Packard®HPL2445w LCD monitor. A general purpose I/O interface 312 interfaceswith a keyboard and/or mouse 314 as well as an optional touch screenpanel 316 on or separate from display 310. General purpose I/O interfacealso connects to a variety of peripherals 318 including printers andscanners, such as an OfficeJet® or DeskJet® from Hewlett Packard®.

A general-purpose storage controller 320 connects a storage medium disk304 with a communication bus 322, which may be an ISA, EISA, VESA, PCI,or similar, for interconnecting all of the components of the computer326. A description of the general features and functionality of thedisplay 310, keyboard and/or mouse 314, as well as the displaycontroller 308, storage controller 320, network controller 306, andgeneral purpose I/O interface 312 is omitted herein for brevity as thesefeatures are known.

FIG. 4 illustrates a flowchart 400 of reflection seismic survey in awireless seismic network within a survey area, according to certainembodiments.

In an initial step, step 402, detecting seismic reflection signals froma seismic energy source 106. In an embodiment, each of the plurality ofwireless seismic sensor nodes (102, 200) is configured to detect seismicreflection signals. In an embodiment, the seismic energy source 106 isconfigured to generate and broadcast radio signals/seismic signals ofpredetermined frequencies towards the surface of the Earth.

Step 404 includes recording of the detected seismic reflection signalsin each of the plurality of wireless seismic sensor nodes (102, 200).

Step 406 includes transmitting the recorded seismic signals as seismicdigital data by the wireless seismic sensor nodes (102, 200) to acentral data receiving device 108. In an embodiment, the wirelessseismic sensor nodes (102, 200) use a combination of OFDMA and TDMA fortransmission of the seismic digital data. In another embodiment, theseismic digital data are transmitted such that the OFDMA subcarriers anda time shot assigned to each wireless seismic sensor node (102, 200)match with the data acquisition parameters of the wireless geophone. Thedata acquisition parameters of the wireless geophone are bandwidth,sampling frequency, bits per sample, and recorded trace duration of theseismic digital data. Each wireless seismic sensor node (102, 200) isconfigured to transmit the seismic digital data at a rate of 48 kbit/secusing TDMA. Each subcarrier in OFDMA has a bandwidth of 3937 Hz, and twosubcarriers per time slot are assigned to one geophone.

The transmission of the seismic digital data is operated in the TVbroadcast bands, and the seismic digital data is transmitted directly tothe central data receiving device 108. During transmitting the seismicdigital data, the seismic digital data recorded per seismic shot istransmitted substantially within 10 seconds after the seismic shot. Thetime slot and subcarriers assigned to each wireless geophone are fixed.The frame size of seismic digital data is divided into frames. Further,the frame size is adjusted based on a signal-to-noise ratio.

Step 408 includes changing the seismic energy source location forseismic reflection. In an embodiment, the seismic energy source 106 isconfigured to generate and broadcast seismic reflection signals ofpredetermined frequencies. In another embodiment, the seismic energysource 106 is a vibrator truck, an air gun, a thumper truck, a plasmasound source, and a seismic vibrator boomer source.

Step 410 includes repeating the detecting, recording and transmitting anumber of times for each change in seismic energy source. In anembodiment, the central data receiving device 108 is configured to checkwhether all the survey area has been covered or not. If any survey areais remaining, the central data receiving device 108 is configured tosend an instruction to the seismic energy source 106 to travel thatremaining part and transmit the seismic signals towards the remainingpart. As there are more than 50,000 wireless geophones, after changingthe position of the seismic energy source 106, more than 50,000reflected signals are recorded by the wireless seismic sensor nodes.

As shown in FIG. 5A, block 502 shows the channel assignment to variouswireless geophones using the OFDMA-TDMA scheme. In the OFDMA-TDMAscheme, a particular wireless geophone is given all the sub-carriers ofthe network for any particular symbol duration. The OFDMA-TDMA schemeschedules multi-geophone transmissions within the time-sub-carrier2-dimensional domain. The sub-carrier and transmission times or symboldurations are allocated to multiple geophones without overlapping sothat multiple users can access the wireless media without mutualinterference to each other. As an example, as shown in block 502, 1440data subcarriers and 95 time slots are used. Therefore, the OFDMA-TDMAscheme in FIG. 5A can accommodate 136,800 (1440*95=136800) wirelessgeophones (indicated by various patterns) to transmit data towards thecentral data receiving device 108, thereby enhancing transmission rate.As mentioned above, the scheme will eventually field onemillion-channels. In addition, the amount of data flowing from itsseismic operations may be between 200 and 400 megabytes per second.

FIG. 5B illustrates a block diagram of seismic data recording andtransmission at a wireless geophone, according to aspects of the presentdisclosure. Block 504 shows a transmitter at the i^(th) wirelessgeophone (seismic data recording and transmission at the i^(th)geophone). At block 506, the i^(th) wireless geophone is configured todetect the presence of the seismic signals and record the detectedseismic signals. Further, at block 508, using the analog-to-digitalconverter the received seismic signals are converted into the seismicdigital data. Furthermore, using an OFDM transmitter at block 510, theseismic digital data is converted into a baseband OFDM signal. Forconversion, the seismic digital data, firstly, the data is modulatedusing modulation scheme such as QPSK, QAM etc. In an embodiment, anumber of modulators are employed to apply multicarrier OFDM modulationto generate a number of modulated data streams. In an embodiment, thenumber of modulated data streams corresponds to the number of carriersof the applied multi carrier OFDM modulation.

The modulated data is processed through a number of Discrete FourierTransformers (DFTs) which are configured to transform the number ofmodulated data streams into the frequency domain. Further, the signal inthe frequency domain is passed by a number of phase rotation blocks,where each phase rotation block is configured to apply a specific phaserotation to each output of a respective DFT. In an embodiment, a numberof subcarrier mappers is employed which are configured to map the outputof the DFTs, as phased rotated by the phase rotation blocks, ontosubcarriers. In last step, at least one Inverse DFT (IDFT) is configuredto transform the output of the DFTs, as mapped onto the subcarriers,back to the time domain. At least one power amplifier is configured toamplify the output of the at least one IDFT.

In another embodiment, the OFDM symbol is constructed in the frequencydomain by mapping the input bits on the I- and Q-components of the QAMsymbols and then ordering them in a sequence with a specific lengthaccording to the number of subcarriers in the OFDM symbol. Using themapping and ordering process, one constructs the frequency components ofthe OFDM symbol. To transmit the signal, the signal must be representedin time domain, accomplished by the inverse fast Fourier transform IFFT.

At block 512, in an embodiment, the radio frequency (RF) front-endmodule is configured to route the RF signals received from the OFDMtransmitter via one or more antennas. Radio frequency (RF) front-endmodules are utilized in the wireless geophones to handle RF signalstransmitted to the wireless geophones and/or received by the wirelessgeophones. The RF front-end module may include RF front-end circuitry,such as antenna switching circuitry, that allows for RF signals to berouted to the various transmit chains and receiver chains from one ormore common antennas. In one embodiment, the RF front-end moduleeliminates additional transmission overhead bits, simplifiestransmission and reception complexity and reduces the signalpeak-to-average power ratio (PAPR).

As shown in FIG. 5C, block 514 shows a receiver at the central datareceiving device 108 for a specific time slot. Using the radio frequency(RF) front-end module at the receiver, the RF signals are received fromthe OFDM transmitter via one or more antennas corresponding to thenumber of wireless geophones.

At block 516, an OFDM demodulator is used for demodulating the receivedsignals at the RF front-end module using the orthogonal frequencydivision demodulation method. The OFDM demodulator can be an inverseoperation of OFDM modulator. Signals received through the RF front endmodule are subjected to a fast Fourier transform (FFT) by the OFDMAdemodulator. The OFDM demodulator outputs a baseband signal whichrepresents of the modulated signal, which was input into the OFDMModulator.

At block 518, a digital to analog converter is used that converts thedigital signal into the analog signal. For example, the digital toanalog converter is configured to convert the received digital data intothe seismic signal for each of the wireless geophone.

At block 520, the output of the digital to analog converter is receivedand displayed as seismic waveform corresponding to each of the wirelessgeophone.

The present disclosure derives the throughput and transmission time fromwireless geophones to the central data receiving device 108 in thewireless seismic network 100 based on OFDMA-TDMA scheme. Transmittingthe seismic digital data using the OFDMA-TDMA scheme requires that theOFDM subcarriers and time shot assigned to each wireless geophone mustmatch with the acquisition parameters, like bandwidth, samplingfrequency, bits per sample, and trace duration (trace length) of theseismic data. In particular, the seismic digital data has a typicalsampling frequency of f_(s)=500 Hz and the trace length of about 6 sec.A 24-bit A/D converter is used that yields a data acquisition rate of 12kbits/sec. The data acquisition rate per wireless geophone is 36kbits/sec. Developing an OFDMA-TDMA (hybrid system)-based wirelessgeophone network of the present disclosure, ensures the timely deliveryof the seismic data in a high dense setup.

In an operative embodiment, the present disclosure operates in TV whitespace, i.e., the IEEE 802.22 standard. As regional area network has arange up to 30 km², therefore, the physical layer system parametersrelated to IEEE 802.22 standard are used. For this standard, the datarate for the Binary Phase Shift Keying (BPSK) in a 6 MHz channel is 4.56Mbits/sec. Since BPSK has a low bit error rate, BPSK is then consideredas the modulation scheme in the present disclosure. Furthermore, in oneOFDM symbol, there are 2048 data carriers out of which 1440 datacarriers are used for data and the rest data carriers (2048−1440=608)for guard and pilots. Further, it is noted that in the 6 MHz channel,the signal bandwidth is 5.67 MHz, which is occupied by 1440 datacarriers.

Now considering the following parameters for seismic data acquisitionand wireless regional area network, the wireless seismic network 100 isdesigned as follows: given that each wireless geophone can transmit dataat a rate of 48 kbit/sec (higher than the minimum 36 kbits/sec) usingTDMA for a total data rate of 4.56 Mbits/sec, results in 95 geophones.Moreover, each subcarrier in OFDMA has a bandwidth of 3937 Hz (signalbandwidth per data carrier in one OFDM symbol). At a particular instant,two subcarriers per time slot are assigned to one geophone to optimizethe Fast Fourier Transform (FFT) processing. In this way, the consideredsetup supports up to 95×(1440/2) geophones with a range of 30 km. Thisarrangement is enough for a typical survey area of around 20 km².

A Markov chain approach is used to model the wireless data transmission,for purposes of initial evaluation. FIG. 6 is a diagram of a statetransition model of seismic digital data transmission, according toaspects of the present disclosure. In FIG. 6 , a transmission state isindicated by 602. 604 represents the first transmission state, and 606represents the second transmission state. The present disclosure employsthe Markov chain to model the transmission of the seismic digital datafrom the wireless seismic sensor node (102, 200) to the central datareceiving device 108. The Markov chain analysis is used to optimizesystem parameters like throughput. A seismic shot data comprises Mframes, where each frame has N information bits. Once the data ofcurrent seismic shot is received successfully by the central datareceiving device 108, the next shot data is transmitted.

The set T is the geophone states while a geophone is transmitting awindow of M recorded frames. The set R_(i) is the geophone state whileit is retransmitting the erroneous or lost frames for the i^(th) time.As shown in FIG. 6 , all the transmission states (602, 604, 606) in eachcolumn are equally probable since the probability of transition betweenthem is one. The state probability distribution vector a II is organizedas follows:

Π=[T

₁

₂

₃ . . . ]^(t),  (1)

where t denotes transpose operation. In the case of three frames to betransmitted, i.e., M=3 as an example, the state probability distributionvector is given as:

Π=[T|R _(1,1) R _(1,2) R _(1,3) |R _(2,1) R _(2,2) R _(2,3)| . . .]^(t),

where T represents the state of transmitting a frame and R_(i,j)represents the i^(th) re-transmission state when j frames are to beretransmitted. Therefore, the corresponding geophone transition matrixwhen M=3, can be set up as:

$\begin{matrix}{{P = \begin{bmatrix}p_{3,0} & p_{1,0} & p_{2,0} & p_{3,0} & p_{1,0} & p_{2,0} & p_{3,0} & \ldots \\p_{3,1} & 0 & 0 & 0 & 0 & 0 & 0 & \ldots \\p_{3,2} & 0 & 0 & 0 & 0 & 0 & 0 & \ldots \\p_{3,3} & 0 & 0 & 0 & 0 & 0 & 0 & \ldots \\0 & p_{1,1} & p_{2,1} & p_{3,1} & 0 & 0 & 0 & \ldots \\0 & 0 & p_{2,2} & p_{3,2} & 0 & 0 & 0 & \ldots \\0 & 0 & 0 & p_{3,3} & 0 & 0 & 0 & \ldots \\ \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \vdots & \ddots \end{bmatrix}},} & (2)\end{matrix}$

where the transition probability p_(i,j) is the likelihood ofretransmitting j frames while i frames are sent, and it is equal to:

$\begin{matrix}{{p_{i,j} = {\begin{pmatrix}i \\j\end{pmatrix}\left( {1 - \sigma} \right)^{i - j}\sigma^{j}}},} & (3)\end{matrix}$

where σ is the probability that one or more bits in a frame are in errorand it is defined as follows:

σ=1−(1−ρ)^(N),  (4)

where ρ=Q(√{square root over (2E_(b)/N_(O))}) is the bit error rate(BER) for Additive white Gaussian noise (AWGN) channel where (Q(.) isthe Q-function, E_(b) and N_(O) are the energy per bit and noisespectral density, respectively.

In case of a fading channel, the received signal is y=hx+z, whereh=αe^(ϕ) is a fading channel coefficient with magnitude α, and phase φ,x is the transmitted signal, and z is white Gaussian noise.

The fading energy per bit is given as |h|²E_(b)/N_(O)=α²E_(b)/N_(O).

Since α is a random quantity, the average BER is calculated with respectto the distribution of α. For the Rayleigh channel, the distribution isF(α)=2αe^(−α) ² . The average BER is calculated by solving the integral:

∫₀ ^(∞) Q(√{square root over (2α² E _(b) /N _(O))})F(α)dα;

Hence, the BER for fading channel is

$\rho = {\frac{1}{2}\left( {\left( {1 - \sqrt{\frac{E_{b}/N_{o}}{1 + {E_{b}/N_{0}}}}} \right).} \right.}$

The state probability distribution vector Π is obtained by solving thefollowing global balance equation:

PΠ=Π,  (5)

with an additional constraint

1Π=1,  (6)

where 1 represents a row vector of ones. Equations (5) and (6) can besolved using MATLAB.

Alternatively, an iterative procedure can be used to find Π, given asbelow.

The state probabilities associated with the r^(th) re-transmission,i.e.,

_(r) are given by the following iterative expression:

$\begin{matrix}{{R_{r,j} = {\sum_{i = j}^{M}R_{r - 1}}},{{ip}_{i,j}\begin{matrix}{{r = 2},3,\ldots} \\{{j = 1},2,{\ldots M}}\end{matrix}}} & (7)\end{matrix}$

and the initial state probabilities associated with R₁ as:

R _(1,j) =Tp _(M,j) j=1,2, . . . M  (8)

Solving for Π Iteratively:

Following equations (7) and (8), all the re-transmission stateprobabilities are expressed in terms of the transmit state probabilityT. The state probability distribution vector Π is obtained iterativelyaccording to:

-   -   Initialize the transmission state with a random number value,        e.g., T=rand.    -   Estimate the re-transmission state probabilities        ₁ using equation (8), and the rest R_(r) (for r>1) using        equation (7).    -   Sum all the transmission and re-transmission state probabilities        in order to satisfy equation (6)

$\alpha = {{MT} + {\sum\limits_{r = 1}^{R_{\max}}{\sum\limits_{i = 1}^{M}{iR}_{r,i}}}}$

-   -   where R_(max) is the maximum re-transmissions allowed, and α is        the normalization constant.    -   Calculate the normalized state probability distribution vector,        e.g., for M=3 and R_(max)=3, as follows:

$\prod{= {\frac{1}{\alpha}\left\lbrack {T{❘{R_{1,1}R_{1,2}R_{1,3}{❘{R_{2,1}R_{2,2}R_{2,3}}❘}R_{3,3}}}} \right\rbrack}^{t}}$

Note that the sizes of P and Π are (MR_(max)+1)×(MR_(max)+1) and(MR_(max)+1)×1, respectively. The state probabilities are useful inderiving the throughput and transmission time expressions.

Performance Measures

The wireless geophone keeps retransmitting the erroneous frames untilall the frames of the current shot are received error-free. Hence, thewireless geophone starts to transmit the next shot data after successfultransmission of current shot data. The average number ofre-transmissions and frames sent during each re-transmission areestimated, thereby, calculating the average delay incurred by a frameand throughput when there are transmission errors. The transmission timefor the whole shot data can then be calculated and the parameters likepacket size can be optimized to perform the acquisition processseamlessly. In the ensuing, key performance indices are derived.

A. Average Number of Re-transmissions A_(n)

The probability of the geophone being in the r^(th) re-transmissionstate has the form:

β_(r)=Σ_(i=1) ^(M) R _(r,i).  (9)

Consequently, the mean number of re-transmissions by the geophone for Mframes (per seismic shot) is found to be:

$\begin{matrix}{A_{n} = {\frac{1}{T}{\sum_{r = 1}^{R_{\max}}{\beta_{r}.}}}} & (10)\end{matrix}$

B. Average Delay D

At the r^(th) re-transmission, the average number of frames sent isobtained according to

n _(r)=Σ_(i=1) ^(M) iR _(r,i)  (11)

The average delay (in terms of frames) associated with a frameretransmitted r^(th) time is comprised of the transmission delay and theaccumulation of all the delays due to re-transmissions. Thus, theaverage delay can be written as

$\begin{matrix}{d_{r} = {M + {\frac{1}{T}{\sum_{j = 1}^{r}{n_{j}.}}}}} & (12)\end{matrix}$

The average delay (in terms of bits) incurred while transmitting apayload bit is the sum of transmitted and retransmitted bits per seismicshot divided by the total payload bits per seismic shot and can be shownto be

$\begin{matrix}{{D = {1 + \frac{H}{N} + \frac{\left( {N + H} \right){\sum_{r = 1}^{R_{\max}}n_{r}}}{NMT}}},} & (13)\end{matrix}$

where H and N are the header size and payload size in bits,respectively, and B=N+H.

C. Average Number of Retransmitted Frames M_(r)

The average number of retransmitted frames shall be determined accordingto

$\begin{matrix}{M_{r} = {\frac{1}{T}{\sum_{r = 1}^{R_{\max}}{n_{r}.}}}} & (14)\end{matrix}$

D. Normalized Throughput (η)

The normalized throughput of the protocol is the ratio of the totalnumber of information bits per seismic shot to the total number of bitstransmitted including re-transmissions and headers, i.e.,

$\begin{matrix}{\eta = {\frac{MN}{\left( {M + M_{r}} \right)\left( {N + H} \right)}.}} & (15)\end{matrix}$

When there are no errors M_(r)=0 and the throughput is maximum, i.e.,

$\begin{matrix}{\eta_{\max} = {\frac{N}{N + H}.}} & (16)\end{matrix}$

FIG. 7 is a diagram of a graph (700) of throughput per geophone versussignal-to-noise ratio, according to aspects of the present disclosure.FIGS. 7, 8, and 9 are plotted for AWGN channel and sampling frequencyf_(s)=500 Hz. In an embodiment, the inter-shot time for the seismicacquisition is 14 sec. Therefore, the data of a seismic shot must betransmitted within this time. To ensure a quick quality check at thecentral data receiving device 108, a strict condition is assumed, i.e.,when a bit in a frame is in error, it is retransmitted. The throughputbetween the wireless geophone and the central data receiving device 108is plotted in FIG. 7 for various frame sizes and signal-to-noise ratio(SNR) per bit levels. As shown in FIG. 7 , for a payload size of N=8bits, both theoretical value and simulation value is the same, indicatedby line 702. In FIG. 7 , for a payload size of N=16 bits, plot line 706illustrates theoretical value, and plot line 704 illustrates simulationvalue of the throughput per geophone. Further, for a payload size ofN=32 bits, plot line 710 illustrates theoretical value and plot line 708illustrates simulation value of the throughput per geophone. As can beseen from FIG. 7 the throughput is lowest for large frame payload sizesof N=8 bits to N=32 bits, and the SNR is low (toward left end of theplot in FIG. 7 ). Conversely, a high throughput is required for higherframe payload sizes in order to achieve a high SNR (toward right end ofthe plot in FIG. 7 ). The reason for this relationship is thattransmitting smaller frames requires more overhead (for whole shot data)but has a beneficial high SNR. On the other hand, larger frames requiremore re-transmissions due to low SNR. The throughput saturates for anyvalue of frame payload size N, however, not attaining the samethroughput value. The throughput saturation happens when the header sizeis fixed having the same information for any payload size. In such case,reducing the payload size results in that the saturated throughput isless due to more overhead.

FIG. 8 is a diagram of a graph (800) of time to transmit data of oneshot to the central data receiving device 108 versus signal-to-noiseratio, according to aspects of the present disclosure.

As shown in FIG. 8 , the total time (in seconds) to transmit the wholedata of t_(s)=6 sec (trace length) by a geophone is found to be

$\begin{matrix}{{D_{s} = \frac{D \times f_{s} \times 24 \times t_{s} \times 95}{2d}},} & (17)\end{matrix}$

where d is the data rate (4.56 Mbits/sec), and the header size is takenas 6 bytes (H=48 bits).

As shown in FIG. 8 , for N (number of information bits)=8, boththeoretical value and simulation value for transmission time is thesame, indicated by line 802. In an embodiment, the inter-shot time forthe seismic acquisition is 14 sec (shown by plot line 812). Thetransmission time is around 10 sec (N=8 bits) when the SNR is 0 dB.Further, for N=16 information bits, plot line 806 illustratestheoretical value and plot line 804 illustrates simulation value of thetransmission time. Further, for N=32 information bits, plot line 810illustrates theoretical value and plot line 808 illustrates simulationvalue of the transmission time taken by each wireless geophone. In asimilar existing system, the transmission time from the wirelessgeophone to the intermediate node (wireless gateway node) was around 50sec at 20 dB SNR with each intermediate gateway node serving 200wireless geophones. Furthermore, the wireless gateway is linked to thecentral data receiving device 108 using a wire.

The time achieved by employing the present disclosure is far better thanusing the random access method by avoiding the need for an intermediategateway node. In the random access method, more time and processingpower is wasted due to sensing the channel, collision, backoff, and thenre-transmission. On the other hand, in the disclosed method, time slotand subcarriers are assigned to the wireless geophone are hardwired(fixed) and, therefore, complexity is much less. Since there is nointermediate node, the interference among the cells served by differentintermediate nodes is also avoided. Hence, improving the overallperformance in terms of time and throughput. Furthermore, the achieved10 sec transmission time is well within the range of the inter-shottime. Hence, the acquisition process performs seamlessly withoutinterruption. Although, a frame with N=8 information bits fulfills therequirements, however, a large packet at high SNR saves resources (alsoless time is required). Therefore, an adaptive frame size can be used.More importantly, the hardware cost is much less than in known prior artbecause no gateway is used.

Next, the re-transmission per shot (900) is depicted in FIG. 9 toillustrate the re-transmission required for various SNR levels. As shownin FIG. 9 , for N (number of information bits)=8, both theoretical valueand simulation value of number of re-transmission is same, indicated byline 902. Further, for N=16 information bits, plot line 904 illustratestheoretical value and simulation value of number of re-transmission(similar). Further, for N=32 information bits, both theoretical valueand simulation value of number of re-transmission is same, indicated byline 906. The actual re-transmission required is compared with themaximum retry limit R_(max) (shown by plot line 908). In order not todrop frames, the average re-transmission A_(n) must be less than themaximum allowed re-transmissions R_(max). As can be seen from FIG. 9 ,the frames are not dropped even with the payload size of N=32information bits (as shown by plot line 906). However, increasing thepayload size results in an increase in the number of retransmissions. Athigh SNR, with no or less bits in error, the number of re-transmissionsapproaches zero. This is regardless of overhead (header).

FIG. 10 is a diagram of a graph (1000) of time to transmit data of oneshot to the central data receiving device versus sampling frequency,according to aspects of the present disclosure. FIG. 10 illustrates theeffect of various sampling frequencies for AWGN and Rayleigh Fadingchannels and comparison with the prior art. As shown in FIG. 10 , forpayload N (number of information bits)=8, both theoretical value andsimulation value of time to transmit data of one shot is same, indicatedby line 1002. Further, for payload N=16 information bits, plot line 1004illustrates time to transmit data of one shot (having similar value oftheoretical result and simulation result). Further, for payload N=32information bits, both theoretical value and simulation value of time totransmit data of one shot is same, indicated by line 1006. It is evidentfrom FIG. 10 that the time to transmit data of one shot is very smallfor the disclosed scheme when compared to that obtained by the existingschemes.

The method of reflection seismic survey of FIGS. 1-5 is in a wirelessseismic network within a large survey area, preferably greater that 20km². The method includes detecting, in each of a plurality of wirelessseismic sensor nodes, seismic reflection signals from a seismic energysource; recording, in each of the plurality of wireless seismic sensornodes, the detected seismic reflection signals; transmitting, by thewireless seismic sensor nodes, the recorded seismic signals as seismicdigital data, using a combination of OFDMA and TDMA, to a central datareceiving device 108; changing the seismic energy source location forseismic reflection; and repeating the detecting, recording andtransmitting a number of times for each change in seismic energy source.

The method further includes transmitting the seismic signals such thatOFDMA subcarriers and a time shot assigned to each wireless seismicsensor node match data acquisition parameters of wireless seismic sensornode of bandwidth, sampling frequency, bits per sample, and recordedtrace duration of the seismic digital data.

The method further includes transmitting the seismic digital data isperformed by each wireless seismic sensor node transmitting data at apredetermined transmission rate using TDMA, where each subcarrier inOFDMA has a predetermined bandwidth, and two subcarriers per time slotare assigned to one wireless seismic sensor node.

The survey area is at least 20 km². The wireless transmission of theseismic digital data is operated in TV broadcast bands, and the seismicdigital data is transmitted directly to the central data receivingdevice.

In transmitting the seismic digital data, the seismic digital datarecorded per shot is transmitted substantially within 10 seconds, a timeslot and subcarriers assigned to each wireless seismic sensor node arefixed, and frame size, of a data stream divided into frames, of seismicdigital data is adjusted based on a signal-to-noise ratio.

The frame size of the seismic digital data has a payload size of 16bits.

The wireless seismic sensor nodes for reflection seismic survey of FIGS.1-5 is in a wireless seismic network within a survey area. Each of aplurality of the wireless seismic sensor nodes includes communicationscircuitry configured to detect seismic reflection signals from a seismicenergy source; a memory for recording the detected seismic reflectionsignals; and the communications circuitry 212 configured to transmit therecorded seismic signals as digital data, using a combination ofOrthogonal Frequency-Division Multiple Access (OFDMA) and Time DivisionMultiple Access (TDMA), to a central data receiving device, wherein thedetecting, recording and transmitting is repeated substantially a numberof times upon changing the source location for the seismic reflectionsignals.

The communications circuitry 212 is further configured to transmit theseismic signals such that OFDMA subcarriers and a time shot assigned toeach wireless seismic sensor node match data acquisition parameters ofwireless seismic sensor node of bandwidth, sampling frequency, bits persample, and recorded trace duration of the seismic digital data.

The communications circuitry 212 is configured to transmit the seismicdigital data at a predetermined transmission rate using TDMA, whereineach subcarrier in OFDMA has a predetermined bandwidth, and twosubcarriers per time slot are assigned to one wireless seismic sensornode.

The survey area is 20 km². The communications circuitry 212 is furtherconfigured to wireless transmit the seismic digital data using TVbroadcast bands directly to the central data receiving device.

The communications circuitry 212 is further configured to transmit theseismic digital data recorded per shot substantially within 10 seconds,wherein a time slot and subcarriers assigned to each wireless seismicsensor node are fixed, and wherein frame size, of a data stream dividedinto frames, of seismic digital data is adjusted by the communicationscircuitry 212 based on a signal-to-noise ratio.

The frame size of the seismic digital data has a payload size of 16bits.

A non-transitory computer-readable storage medium of FIGS. 1-5 storinginstructions for reflection seismic survey in a wireless seismic networkwithin a survey area, processing circuitry, in each of a plurality ofwireless seismic sensor nodes, executes the instructions according to amethod including

detecting, in each of a plurality of wireless seismic sensor nodes,seismic reflection signals from a seismic energy source;

recording, in each of the plurality of wireless seismic sensor nodes,the detected seismic reflection signals;

transmitting the recorded seismic signals as seismic digital data, usinga combination of Orthogonal Frequency-Division Multiple Access (OFDMA)and Time Division Multiple Access (TDMA), to a central data receivingdevice;

monitoring a change in the seismic energy source location for seismicreflection; and

repeating the detecting, recording and transmitting a plurality of timesfor each change in seismic energy source.

The non-transitory computer-readable storage medium further includestransmitting the seismic signals such that OFDMA subcarriers and a timeshot assigned to each wireless seismic sensor node match dataacquisition parameters of wireless seismic sensor node of bandwidth,sampling frequency, bits per sample, and recorded trace duration of theseismic digital data.

The non-transitory computer-readable storage medium further includestransmitting the seismic digital data is performed by each wirelessseismic sensor node transmitting data at a predetermined transmissionrate using TDMA, where each subcarrier in OFDMA has a predeterminedbandwidth, and two subcarriers per time slot are assigned to onewireless seismic sensor node.

The survey area is at least 20 km². The wireless transmission of theseismic digital data is operated in TV broadcast bands, and the seismicdigital data is transmitted directly to the central data receivingdevice.

In transmitting the seismic digital data, the seismic digital datarecorded per shot is transmitted substantially within 10 seconds, a timeslot and subcarriers assigned to each wireless seismic sensor node arefixed, and frame size, of a data stream divided into frames, of seismicdigital data is adjusted based on a signal-to-noise ratio.

The frame size of the seismic digital data has a payload size of 16bits.

The above-described hardware description is a non-limiting example ofcorresponding structure for performing the functionality describedherein.

Obviously, numerous modifications and variations of the presentdisclosure are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thedisclosure may be practiced otherwise than as specifically describedherein.

1. A method of reflection seismic survey in a wireless seismic networkwithin a survey area, the method comprising: detecting, in each of aplurality of wireless seismic sensor nodes, seismic reflection signalsfrom a seismic energy source; recording, in each of the plurality ofwireless seismic sensor nodes, the detected seismic reflection signals;transmitting, by the wireless seismic sensor nodes, the recorded seismicsignals as seismic digital data, using a combination of OrthogonalFrequency-Division Multiple Access (OFDMA) and Time Division MultipleAccess (TDMA), to a central data receiving device; changing the seismicenergy source location for seismic reflection; and repeating thedetecting, recording and transmitting a number of times for each changein seismic energy source.
 2. The method of claim 1, further comprising:transmitting the seismic signals such that OFDMA subcarriers and a timeshot assigned to each wireless seismic sensor node match dataacquisition parameters of wireless seismic sensor node of bandwidth,sampling frequency, bits per sample, and recorded trace duration of theseismic digital data.
 3. The method of claim 1, wherein the transmittingthe seismic digital data is performed by each wireless seismic sensornode transmitting data at a predetermined transmission rate using TDMA,where each subcarrier in OFDMA has a predetermined bandwidth, and twosubcarriers per time slot are assigned to one wireless seismic sensornode.
 4. The method of claim 1, wherein the survey area is at least 20km², and wherein the wireless transmission of the seismic digital datais operated in TV broadcast bands, and the seismic digital data istransmitted directly to the central data receiving device.
 5. The methodof claim 1, wherein in transmitting the seismic digital data, theseismic digital data recorded per shot is transmitted substantiallywithin 10 seconds, a time slot and subcarriers assigned to each wirelessseismic sensor node are fixed, and a frame size, of a data streamdivided into frames, of seismic digital data is adjusted based on asignal-to-noise ratio.
 6. The method of claim 5, wherein the frame sizeof the seismic digital data has a payload size of 16 bits.
 7. A systemhaving wireless seismic sensor nodes for reflection seismic survey in awireless seismic network within a survey area, each of a plurality ofthe wireless seismic sensor nodes comprising: communications circuitryconfigured to detect seismic reflection signals from a seismic energysource; a memory for recording the detected seismic reflection signals;and the communications circuitry configured to transmit the recordedseismic reflection signals as seismic digital data, using a combinationof Orthogonal Frequency-Division Multiple Access (OFDMA) and TimeDivision Multiple Access (TDMA), to a central data receiving device,wherein the detecting, recording and transmitting is repeatedsubstantially a plurality of times upon changing the source location forthe seismic reflection signals.
 8. The system of claim 7, wherein thecommunications circuitry is further configured to transmit the seismicreflection signals such that OFDMA subcarriers and a time shot assignedto each wireless seismic sensor node match data acquisition parametersof wireless seismic sensor node of bandwidth, sampling frequency, bitsper sample, and recorded trace duration of the seismic digital data. 9.The system of claim 7, wherein the communications circuitry isconfigured to transmit the seismic digital data at a predeterminedtransmission rate using TDMA, wherein each subcarrier in OFDMA has apredetermined bandwidth, and two subcarriers per time slot are assignedto one wireless seismic sensor node.
 10. The system of claim 7, whereinthe survey area is at least 20 km², and the communications circuitry isfurther configured to wireless transmit the seismic digital data usingTV broadcast bands directly to the central data receiving device. 11.The system of claim 7, wherein the communications circuitry is furtherconfigured to transmit the seismic digital data recorded per shotsubstantially within 10 seconds, wherein a time slot and subcarriersassigned to each wireless seismic sensor node are fixed, and whereinframe size, of a data stream divided into frames, of seismic digitaldata is adjusted by the communications circuitry based on asignal-to-noise ratio.
 12. The system of claim 11, wherein the framesize of the seismic digital data has a payload size of 16 bits.
 13. Anon-transitory computer-readable storage medium storing programinstructions for reflection seismic survey in a wireless seismic networkwithin a survey area, processing circuitry, in each of a plurality ofwireless seismic sensor nodes, executes the program instructionsaccording to a method comprising: detecting, in each of the plurality ofwireless seismic sensor nodes, seismic reflection signals from a seismicenergy source; recording, in each of the plurality of wireless seismicsensor nodes, the detected seismic reflection signals; transmitting therecorded seismic signals as seismic digital data, using a combination ofOrthogonal Frequency-Division Multiple Access (OFDMA) and Time DivisionMultiple Access (TDMA), to a central data receiving device; monitoring achange in the seismic energy source location for seismic reflection; andrepeating the detecting, recording and transmitting a number of timesfor each change in seismic energy source.
 14. The non-transitorycomputer-readable storage medium of claim 13, further comprising:transmitting the seismic signals such that OFDMA subcarriers and a timeshot assigned to each wireless seismic sensor node match dataacquisition parameters of wireless seismic sensor node of bandwidth,sampling frequency, bits per sample, and recorded trace duration of theseismic digital data.
 15. The non-transitory computer-readable storagemedium of claim 13, wherein the transmitting the seismic digital data isperformed by each wireless seismic sensor node transmitting data at apredetermined transmission rate using TDMA, where each subcarrier inOFDMA has a predetermined bandwidth, and two subcarriers per time slotare assigned to one wireless seismic sensor node.
 16. The non-transitorycomputer-readable storage medium of claim 13, wherein the survey area isat least 20 km², and the wireless transmission of the seismic digitaldata is operated in TV broadcast bands, and the seismic digital data istransmitted directly to the central data receiving device.
 17. Thenon-transitory computer-readable storage medium of claim 13, wherein intransmitting the seismic digital data, the seismic digital data recordedper shot is transmitted substantially within 10 seconds, a time slot andsubcarriers assigned to each wireless seismic sensor node are fixed, andframe size, of a data stream divided into frames, of seismic digitaldata is adjusted based on a signal-to-noise ratio.
 18. Thenon-transitory computer-readable storage medium of claim 17, wherein theframe size of the seismic digital data has a payload size of 16 bits.